Generation of IL-2-dependent cytolytic T lymphocytes (CTLs) with altered TCR responses derived from antigen-dependent CTL clones

Ag-specific CD8(+) CTL clones require TCR stimulation to respond to IL-2 fo r growth, Because IL-2 may be produced in the vicinity of CD8(+) CTLs when Ag is limiting at the end of an immune response, we have examined the effec t of culturing viral-specific CTL clones in IL-2 in the absence of antigeni c stimulation. Limiting dilution analysis revealed a high precursor frequen cy for CTL clones derived from IL-2 propagation (termed CTL-factor dependen t (FD)) that are dependent upon exogenous IL-2 for growth and survival and no longer require TCR stimulation to proliferate. Culturing CTL-FDs with in fected splenocytes presenting Ag and IL-2 did not revert the clones but did lead to a TCR-induced inhibition of proliferation. The derived CTL-FDs hav e lost the ability to kill via the perforin/granule exocytosis mechanism of killing, although they express similar levels of TCR, CD3 epsilon, CD8 alp ha beta, CD45, and LFA-1 compared with the parental clones. The CTL-FDs ret ain Fas ligand/Fas-mediated cytotoxicity, and IFN-gamma production and regu late the expression of CD69 and IL-2R alpha when triggered through the TCR, A parental CTL protected BALB/c mice from a lethal challenge of influenza virus, whereas a CTL-FD did not. These findings represent a novel regulator y function of IL-2 in vitro that, if functional in vivo, may serve to down- regulate, cellular immune responses.